I feel it's important to seal the wefts before sewing down the tracks to minimize sheding. The hair is so fine and no amount of thread will keep it from sliding off the tracks. Sometimes the wefts are so poorly sewn, I have to result to crazy glue to seal them.
There's other methods out there but in this video I used Clear Acrylic Sealer. With this sealer I still experienced shedding and ultimately had to go over all my tracks with crazy glue. I prefer crazy glue than bonding glue because bonding glue takes too long to dry.